Automatic control device for the regeneration of ion-exchange resins

ABSTRACT

A device for automatically controlling the regeneration of an ion-exchange resin. Two pairs of electrodes are spaced in the resin, one above the other. A variation in capacitance or resistance between the pairs, due to change in ion content of the resin actuates a relay which initiates regenerization. A diode and a strong capacitor retard the relay to avoid the accumulation of false information.

1151 3,652,910 {45} Mar.28, 1972 56] References Cited UNITED STATESPATENTS THE REGENERATIO'N OF ION- EXCHANGERESINS United States PatentUrbain w41 AUTOMATIC CONTROL DEVICE FOR tdllllll l kspaced in thcpacilance or reduc lo change in ion content Of the gcnerizalion. A diodey to avoid the accumulag the rcgcncration of an softening of water.

In such apparatus,` the liquid from which it is desired to eliminate oneor more ions flows through an ion-exchange resin, judiciously chosen sothat an Aexchange of ions between the liquid and the resin takes place.There'are numerous applications of this technique, notably in softeningwater. ln that case, the resin is charged with sodium (Na+) ions and ispermeatedby water to be purified, whereby exchange between the ions(mainly calcium (Ca++) ions) in the water and the sodium ions in theresin takes place. The latter thus progressively becomes charged withthe calcium ions and must be -regenerated to be used again. Regenerationis produced by washing the calcium ion charged resin with asolutioncharged with sodium ions, such as sodium chloride solution.

The present invention thus has'for its 'object to provide an automaticcontrol device. for such regeneration of ionexchange resins, chargedwith ions'collected from a liquid in the course of purification. lnorder to simplify the description,

reference-will be made hereafter tothe case of watersoften'- ing, thatis the elimination of calciumiions from the water by, exchange withsodium ions from the resin,` it being understood l that the invention isapplicable toA all cases of purification of liquids by passage lthroughion-exchange resins.

lt is obviously of interestfthat the regeneration of the resin can becarried out automatically, since the resinhaslost an important part o f'its activity. The devices used so far to achieve such automation arebased upon measurement of the i difference between the electricalconductivity of the'pure v water and of the fresh' resin, on one hand,and the electricalconductivity of the untreated water and the calciumion charged resin, onthe'other hand. For this purpose, electrodes areintroduced at different heights from the bed. of resin and theresistance between the electrodes measured. This resistance, which isproportional to the activity of the resin and the degree of purificationof the water, allows automatic conv trol of regeneration.

Another control technique for' the regeneration of ionexchange resinconsists of adapting a timing device to the apparatus. This timingdevice initiates regeneration after a determined time lapse and for aduration necessary for the exchange ofions.

Anotherfmethod consists of combining'a timing device and the variationin capacity of condensers formed by the resins and electrodes located inthe midst of the resin', and the timing device acts only when the resinneeds to be regenerated, that being controlled by the variation incapacitance.

Many automatic control devices based on these principles' are known, butthey are not entirely satisfactory. v

ln fact, it often happens that the'resin is not disposed in the purifieras an absolutely homogenous bed, but with preferential routes orpassages for the water. In other cases, ionic flows may be producedabove all in the case of high rates of flow of water. lt thus happensthat the electrodes detect saturation of the resin with calcium ions,long before such saturation vhas been achieved. This detection isregistered and regeneration of the resin commenced on'the basis of falseinformation.

On the other hand, in the case of abnormally high water consumption,regeneration of the resin takes place relatively soon after the previousregeneration. The space of time between the successive regenerationscanno't be sufficient for i the formation of a solution properlysaturated with sodium ions. ln consequence, the calcium ion chargedresin is washed The present invention has for its object to remedy thesedifferent defects and to assure efficient regeneration of theionexchange resin.

According to the present invention, an automatic control device for theregeneration of ion-exchange resins by the passage of a liquidtherethrough comprises essentially two pairs of electrodes introducedone below the other in a bed of the resin, a threshold amplifier toamplify the voltage due to the variation in detection of electricalproperties at the level of the two pairs of electrodes a 4regenerationcontrol relay, the

. actuation of which is caused by the amplifier, a diode and a strongcapacitance retarding the moment, of actuation of the relay, the diodeavoiding accumulation of false information.

. The two pairs of electrodes-located one below the other in. the bed ofresin are in the presence of a medium-constituted by theion-exchangeresin and-watenAs the resin gives up its sodium ions to thewater and fixes calcium vions from the latter, the medium at the levelof the upperpair of electrodes is different from the medium at the levelof the lower pair of electrodes. This difference gives rise to avariation in the relationship between the electrical properties of thesetwomedia. Thus, the variation of the relationship between the resistanceof the first pair of electrodes and the resistance of the second pair ofelectrodes is used as the principle lof detection.

But one could also, following another variant ofthe present invention,luse each pair of electrodes-assembled into rigid unit lto provide acondenser where thewater and ther resin between the electrodes of eachpair are dielectric; in this case, the

variation'of capacitanceis used as the principle of detection.

y apparent from the following description of two embodiments by a sodiumsalt solution which is too dilute, and the resin is v not regenerated.The result is that after passage of the solution, theldetector functionsimmediately thereafter, and the.

washing cycle takes place oncemore so that all the time is taken up withregeneration.

of the invention illustrated the accompanying drawings wherein: f

FIG. vlshows two pairs of electrodes and a circuit diagram of a controlcircuit for the regeneration-of a resin; and

FIG.' 2 shows two electrolytie condensers for association with the sameelectrical circuit as in FIG. l.

. The apparatus used (not shown) for softening lwater is filled with anion-exchange resin, which gives up its sodium ions to water andfixescalcium ions from the water. Regeneration of the resin must take.place when it contains no more exchangeable ions of sodium and ispractically saturated with calcium ions.

According to FIG. 1, the instant at which theresin has lost the greaterpart ofits effectiveness is determined by using two pairs of electrodesEl, E2 on one hand and E3, and E, on the other hand which are introducedinto the resin. The pair El, E2 is placed above the pair E3, E4. Theseelectrodes are supplied with alternatingcurrent, to avoid a polarizingeffect. ElectrodeE4 is introduced at a level such that the quantity ofresin located therebelow is sufficient for a normal determinedconsumption, for example a normal days consumption. On the other hand,the resin is charged with calcium ions insuccessive layers, that is theexchange of its ions with those of the water proceeds from the summitofthe resin bed, takes place first in the upper layer of the resin, thenthat layer having been exhausted, the layers located therebelow aresuccessively acted upon. The electrode E4 must not therefore beintroduced into the upper part of the resin otherwise it will detectexhaustion lof the resin longbefore it is completely exhausted. Thedistance between the electrodes El, E2 is identi- -cal to that betweenthe electrodes E3, E4 but the distance between the electrodes E2 and E3is much greater. The distance may be determined as a function -of theflow rate of the watei and of the diameter of the apparatus containingthe resin.

When the resin is practically void of calcium ions, that is when it isfresh or has just been regenerated, the resistance sistances varies. ToIdetect this variation, as is known, a Wheatstone'bridge is formed with aresistance R of the electrodes E E2 designated by R(E E2), theresistance R of electrodes E3, E., by R(E3, E4), a resistor R, and apotentiometer Rh. In this way, when resistance R(E E2) varies, itproduces instability in the bridge.

This instability is very feeble and the voltage delivered is only a fewmillivolts. The voltage is balanced by rectifier bridge D and integratedby a capacitor C,.

A divider bridge formed by resistance R2 and R3 at the base ofTransistor T determines a saturation current on the collector thereof.The voltage of the latter is thus very weak. The integrated voltagecounters the bridge R2, R3. When this integrated voltage is sufficientthe collector current leaves the transistor T. At this moment thevoltage is a maximum at the collector of Transistor T. This voltage isintegrated by diode D capacitor C3, and resistance R5.

These elements are provided to avoid all premature regenerations of theresin, due for example to anfionic stream or the presence ofpreferential routes for the water through the bed of resin. Theseelements create a time constant, that is a delay between detection andregeneration.

Notably there is used a strong capacitor C3, and a diode vD,. This diodeD, is nonconductive and acts as a resistor during the charging ofcapacitor C3. The voltages integrated to the terminals of C3 attacks athreshold amplifier of very high impedance, AHI, which itself controls arelay Re. High impedance amplifier AHI comprises a first transistor X, asecond transistor Y and requisite resistors as is known. As soon as lthevoltage on the terminals of C3 attains the threshold of the amplifier,the relay Re closes, sending on one hand an alternating holding currentto the bridge rectifier D and on the other hand, the alternating currentof the network to the motor M which is provided with a speed reducer.From this moment, motor M runs and, with the cam N closes themicroswitch M which breaks the current to the detection circuit andstops rotation of the motor M. On the other hand, the microswitch M,sends current from the network to the microswitch M2 which reestablishessupply to motor M at the time chosen for regeneration. The microswitchM2 is controlled by a rotating timing device J.

A cam N2 of the motor M controls the cycles of a hydraulic vane so that,the cam having made one complete turn, the resin is regenerated. Themicroswitch M, returns to its initial position and the electroniccircuit is once more completed. A network of 220 volts connects to thecircuit ata, b. C is a rectifier bridge which rectifies voltage of 220volts delivered from transformer F. v The periods of regeneration can bespaced in time as a function of the least time required for thepreparation of a saturated aqueous solution of a sodium salt for the useof the regeneration of the resin. This minimum period is thus also theleast period between two regenerations for which the timing device J isadapted.

In certain cases, water can imprint certain preferred routes through theresin. lt arrives therefore in contact with the electrodes E E2 withouthaving exchanged its calcium ions for sodium ions from the resin. As aresult, the pair of electrodes E E2 indicates that the sodium ions areexhausted from the resin. But this detection is not transmitted directlyto the relay RP, due to the presence of diode D, acting as a resistanceand the strong capacitor C3, that is due to the time constant; and waterhaving followed the preferred route, arrives at the electrodes E3, E,before the relay has closed. In consequence, the two pairs of electrodesare in the presence of the same quality of water, and the relationshipbetween the resistance R(E E2) and R(E3, E3) remains normal, andWheatstone bridge remains balanced. Therefore, regeneration is notinitiated.

lf instead of diode D a linear resistance were used, there would be arisk of the relay closing prematurely. In fact, by using a linearresistance and taking into account the time constant, the discharge ofcapacitor C3 will be very slow. If during the discharge, the consumptionof water is halted, the electrodes E E2, E3, E4 are once more in thepresence of water not containing calcium ions. When consumption againstarts, the two pairs of electrodes will be in the presence of differentqualities of water and capacitor C3 will again be charged. Now thiscapacitor not having been completely discharged, there will be anaccumulation of voltage. If the cycle is repeated` the voltage willeventually reach the amount required to close the relays through theamplifier AHI.

Using a diode D, instead ofa linear resistance, this accumulation ofvoltage is avoided. When the discharge of capacitor C3 ,takes place,diode D, becomes conductive and the discharge is very rapid. It takesplace across the transistor T with use of resistance R5 to limit thecurrent and protect the transistor.

A commutator switch I is also provided which allows special regenerationat any desired time. Due to this commutatona negative supply voltage issent across resistance R3 to capacitor C3 which actuates relay Re. andstarts regeneration.

The circuit controlling regeneration as a function of the detectioncarried out by the two pairs of electrodes also comprises otherelements, such as a diode D2 protecting the amplifier AHI, a stabilizingcondenser C3 for avoiding trembling of the relay R2,a filter C., in thesupply to the transistors, and a capacitor C2 for avoiding alternatecurrent on the diode D,. The `mechanical registration of the detectionremedies all failures of the electric supply network. ln fact, if thedetection takes place for example very early in the morning, andvregeneration is not required until the following night, a very long timeseparates the two functions and it is necessary for the detection to bekept up during that time. But the detection is not useful if consumptionof water continues.

If a suspension of electrical power takes place during a period suchthat the consumption of water may have been significant, no detectionwill take place until the current is restored. In fact, the electrodeswill be in the presence of resin saturated with calcium ions and impurewater, with no difference in electrical conductivity. The resin isexhausted and detection will not take place. On the contrary, if thedetection is registered by a mechanical device, a current stoppageproduced after the detection cannot delay regeneration from the chosentime until the reestablishment of the current supply.

FIG. 2 represents another mode of carrying out the invention whereinelectrolytic condensers are used. The water and the bed of resinconstitute a dielectric.

The value of the capacitance is a function of the surface area of thecondensers, of the distance therebetween and of the dielectric. Thelatter presents different values as a function ofthe state of theion-exchange resin.

Condensers A, and A2 are connected in series and supplied by analternating current U delivered through a transformer. The current whichcrosses the condensers A, and A2 is identical as they are connected inseries. The value of this current depends upon the values of theimpedance and frequency of Z, and Z2. This current is out of phase withthe current U by a certain value, this value depending on Z, and Z2,that is on the capacitance and on the resistance of A, and A2. Thepotential of junction point O' of the two impedances Z Z2 thus has avalue and a phase determined by reference to point O.

In order to compensate for the stray capacitances of the wiring of theprobe and for inequalities of manufacture of the condenser, the point Ois constituted by a potentiometer, to obtain a more precise regulation.This potentiometer comprises a resistance and a rheostat.

The circuit has the appearance of a Wheatstone bridge, its functionbeing to balance the points O and O' in voltage and in phase.

When water-and the ion-exchange resin are charged principally withcalcium ions at the level of condenser A, the impedance thereof varies,this variation being principally due to the resistance to leakage.

It is notable that the leakage resistance has only a weak incidence withreference to the variation in capacitance; on the other hand, as soon asthe electrodes are oxidized, the leakage resistance is very high, thevariation very weak, and only the variation in capacitance may besatisfactorily determined. This peculiarity permits the use of any metalfor the condensers, and enables the apparatus to be as sensitive as newfor several years.

The variation of the relationship of the impedance produces an imbalanceof the bridge, and the voltage as a result is cornpensated (rectifierbridge D) and integrated (capacitor C1) as in the case of the embodimentof FIG. l, since the same means of amplification and control ofregeneration is used.

Other modifications and additional components may be used in the devicesdescribed hereinabove without departing from the scope of the invention,of which the principal advantages are a small power consumption,reliability in use, and efficiency.

What is claimed is:

l. An automatic control device for the regeneration of an ion-exchangeresin, said device comprising two pairs of electrodes positioned withina bed of said resin, a first of said pairs being positioned upstream ofthe other of said pairs; a Wheatstone bridge detection circuit, the fourlegs of which respectively comprise said first pair of' electrodes, saidsecond pair of electrodes, a rheostat and an auxiliary resistance, saiddetection circuit adapted to produce avoltage when the electrical takesplace, said diode further adapted to avoid accumulation of falseinformation; acam mounted on said motor and movable whensaid motoroperates; a first microswitch adapted to be closed by said cam when saidmotor rotates, a second microswitch and a rotating timing device, saidfirst microswitch when closed adapted to break current to saiddetectioncircuit and thereby stop the operation of said motor,

l but also adapted to send current through said second properties ofsaid resin at the levels of said pairs of electrodes f differ; athreshold amplifier connected to amplify said voltage; a relay operablein response to said amplified voltage; a motor for operating saidregeneration and selectively actuated by said relay; a diode andcapacitor means associated with said amplifier and relay for retardingthe operation of said relay and thereby selectively delaying thecommencement of said regeneration, said capacitor being charged by thelow inverse current of said diode and thus having a low charge, and saiddiode being conductive when the discharge of said capacitor microswitchby means of said rotating timing device whereby said motor is againoperated.

2. A device according to claim l characterized in that the distancebetween said two pairs of electrodes is greater than the distanceseparating said electrodes of each pair.

3. A device according to claim l, further comprising a bridge rectifierto rectify said voltage and a capacitor to integrate the rectifiedvoltage.

4. A device according to claim 1 characterized in that the resistanceformed by one pair of said two pairs of electrodes, the resistanceformed by the other pair of said two pairs of electrodes, said rheostatand said auxiliary resistance form said four legs of said Wheatstonbridge, to create said voltage in the case of variation of therelationship between the resistances of said pairs of electrodes.

5. A device according to claim 1 characterized in that the twoelectrodes of each pair of electrodes are assembled into a rigid unitproviding a condenser where the water and the resin between theelectrodes of each pair are the dielectric.

6. A device according to claim 5, characterized in that the capacitanceformed by A one of said condensers, the capacitance formed by the otherof said condensers, said rheostatand said auxiliary resistance form saidfour legs of said Wheatstone bridge, to create said voltage in the caseof variation in the relationshipbetween the impedance of said onecondenser and the impedance of the said other condenser.

1. An automatic control device for the regeneration of an ionexchangeresin, said device comprising two pairs of electrodes positioned withina bed of said resin, a first of said pairs being positioned upstream ofthe other of said pairs; a Wheatstone bridge detection circuit, the fourlegs of which respectively comprise said first pair of electrodes, saidsecond pair of electrodes, a rheostat and an auxiliary resistance, saiddetection circuit adapted to produce a voltage when the electricalproperties of said resin at the levels of said pairs of electrodesdiffer; a threshold amplifier connected to amplify said voltage; a relayoperable in response to said amplified voltage; a motor for operatingsaid regeneration and selectively actuated by said relay; a diode andcapacitor means associated with said amplifier and relay for retardingthe operation of said relay and thereby selectively delaying thecommencement of said regeneration, said capacitor being charged by thelow inverse current of said diode and thus having a low charge, and saiddiode being conductive when the discharge of said capacitor takes place,said diode further adapted to avoid accumulation of false information; acam mounted on said motor and movable when said motor operates; a firstmicroswitch adapted to be closed by said cam when said motor rotates, asecond microswitch and a rotating timing device, said first microswitchwhen closed adapted to break current to said detection circuit andthereby stop the operation of said motor, but also adapted to sendcurrent through said second microswitch by means of said rotating timingdevice whereby said motor is again operated.
 2. A device according toclaim 1 characterized in that the distance between said two pairs ofelectrodes is greater than the distance separating said electrodes ofeach pair.
 3. A device according to claim 1, further comprising a bridgerectifier to rectify said voltage and a capacitor to integrate therectified voltage.
 4. A device according to claim 1 characterized inthat the resistance formed by one pair of said two pairs of electrodes,the resistance formed by the other pair of said two pairs of electrodes,said rheostat and said auxiliary resistance form said four legs of saidWheatston bridge, to create said voltage in the case of variation of therelationship between the resistances of said pairs of electrodes.
 5. Adevice according to claim 1 characterized in that the two electrodes ofeach pair of electrodes are assembled into a rigid unit providing acondenser where the water and the resin between the electrodes of eachpair are the dielectric.
 6. A device according to claim 5, characterizedin that the capacitance formed by one of said condensers, thecapacitance formed by the other of said condensers, said rheostat andsaid auxiliary resistance form said four legs of said Wheatstone bridge,to create said voltage in the case of variation in the relationshipbetween the impedance of said one condenser and the impedance of thesaid other condenser.